My Verditius mage-farmer is looking at making the equivalent of greenhouse in caves.
One of the enchantment he will have to prepare is simply to bring light in these place.
According to the CrIg guidelines, base is 5 for a light as bright as direct sunlight. He needs to adjust it to the size of the greenhouse and done.
However, he is wondering if this light will have any effect on creature which are sensitive to sunlight, like some trolls or vampires.
The fact that sunlight is able to damage or even outright kill some creatures is likely due to some mystical properties of the sun, and the sun is beyond the Lunar Sphere.
He is exploring several possibilities:
the most simple one, real sunlight is a higher magnitude than just "as bright as sunlight". But by how much ?
it is mystical effect, and Vim should be a requisit. It could be a solution, but if it is really a mystical effect, considering that the Sun is outside the Lunar Sphere, throwing a Vim requisit to solve the problem seems inadequate
it is only achievable by Holy magus. A possibility considering the purifying properties linked to the sun.
it is beyond any magic. It is a dead end, but I could see argument for it.
As a side note, I guess that within the Medieval paradigm, having a light "as bright as direct sunlight" is good enough to grow plant underground and there is no additional requisit or magnitude to have the growth effect provided by the sun.
Alternatively, if only real sunlight can make plant grows, could a ReIg be used to transfer the light from the surface underground ? It will allow the undeground garden to follow the normal season.
I know that there is various Cr/Re He spells to make trees blooms and bear fruits within a day, but I also want to be able to have unwarped undegroung biomes following a normal cycle.
Well, just as a one-off thought: magic can make plants grow just fine, in terms of CrHe or ReHe effects; therefore, if sunlight is a necessary part of plant growth in Aristotillean philosophy, then it's likely a "natural" property of the world, and thus can be created/controlled by magic just fine.
In terms of supernatural creatures and their weakness to it - that's usually faries, whose weaknesses are an innate property of themselves for thematic/storytelling purposes - thus the origin of the iron/silver/sunlight/whatever isn't particularly relevant, as long as its suitably dramatic and appropriate.
In terms of some types of demons being weak to sunlight - see above. that's likely a farie pretending to be a demon.
Vulnerability to sunlight is listed in Realms of Power: Infernal as a common demonic weakness, and it's also common in the walking dead (Realms of Power: Magic). I'm not addressing the OP's problem, but I think it's important to note that vulnerability to sunlight is not indicative of faerie.
I'll be the one to throw the wrench: it may be that the mystic effects of sunlight is unique to the sun's actual light. Hermetic Magic cannot affect things beyond the Lunar Sphere, and it could be that certain effects of solar light are beyond sub-lunar magical power. The question then, I suppose, is what is that non-reproducible effect?
There is one possible argument - although it is a stretch - that could support Vim as the closest form related to astronomical phenomenon: in Hermetic Astrology (The Mysteries), it is the form used to assess the astrological time.
Although I am seeing that as a possible way to replicate Sunlight effect, I am not comfortable with this option because de facto, it is opening the door to magic beyond the Lunar Sphere.
Maybe trying to replicate the effect of the Sun on certain supernatural creatures could be a lead for a breakthrough to go beyond the Lunar Sphere or to discover a new Form.
So for now, CrIg to create light to allow the growth of plant is ok using the CrIg Base 5 guideline. However:
there is nothing in the guideline regarding mystical effect of the sun on certain creature and how to replicate it
the Sun is clearly beyond the Lunar Sphere
... thus hermetic magic cannot replicate simply this effect with CrIg.
I would propose a CrIg (PeVi requisit, with Realm specified) which could have the desired effect as long as it penetrates and follows the typical guideline of PeVi against supernatural creature:
Cr(Pe)Ig(Vi) - Banishing light of the Most Uncleaned Ones / Faerie Courts / Void's Minions
Base 5, Touch (+1), Sun (+2), Room (+2), requisit (+2)
Create a light surrounding the caster. Any creatures from the specified Realm loose a number of Might point equal to the spell level -25. The spell must penetrate.
Considering the relatively high level and the casting total to have a decent penetration, it is not really efficient, except to drive away weak creatures. Cheaper than a Aegis, much more limited, but could have its uses when exploring certain areas. It is probably useful when setting camp to make sure that during the night no imp/goblin/spirit comes to pester the group.
Controlling moon and starlight is part of canonical spell in the core rules, albeit, it doesn't have an actual guideline, but the Light Shaft of the Night spell collects moonbeams and starlight into a single shaft of light. It's not much of a jump, IMO, that you could do the same with sunlight. And then, since you can control sunlight with ReIg, I don't have much of a problem of creating it with CrIg.
Creating the light doesn't actually touch anything beyond the Lunar sphere, just as the spell doesn't, since the light is in our sphere now, even though it was created beyond the Lunar Sphere.
My instinctual reaction would have been to say "ooh, sunlight special! Beyond Lunar Sphere! No CrIg!" But if the sunlight itself is special then why not moonlight and starlight too? And then no ReIg of these things. So if Ignem applies for Rego, then also for Creo. The argument that the ability to control but not create a human being acts as precedent does not hold, because both Co and Me are necessary yet insufficient to account for all that goes into a person, so that it is possible for Hermetic magic to control Co and Me aspects of a person but not touch a person's soul, and even Co/Me can be limited by Essential Nature.
That said, I can imagine that someone might want to rule that sunlight affects vampires because it comes from the sun (thou art an accursed enemy of the sun, and shall perish utterly if aught of the sun shall touch thee, even the smallest part) and not because it is any particular kind of light (though we do not understand how this can be, laboratory tests indicate that your cellular structure unravels when subject to particular combinations of electromagnetic radiation...) Then CrIg creates light that is identical to sunlight yet has no adverse effect on vampires because it does not actually come from the sun, but ReIg can collect actual sunlight in a pouch, to be released at need.
Not to undermine my own, halfhearted, argument, but I suspect the reason that vampires are affected by sunlight is that they're faeries, and the stories say they are so affected.
(That said, most vampire stories before the 20th C. do not particularly dwell on the effect of sunlight. It mostly just is a limitation, not a strong bane - the burning effect originates in late 20th C. Hollywood.)
Other variation: would magically-created silver still act as silver (against silver-vunerable faries and demons and whatnot) if it was created via a CrTe? My initial thought is "yes - if it is temporary, it would have to beat their magic resistance; but if it was created with vis, then it would otherwise be normal."
So that would be my solution - if it's temporary sunlight, then it will act as sunlight, but you'll have to beat the target's Might or magic resistance. If you create the sunlight with vis, the it will be 'normal' sunlight, and do whatever it does to the creature without the creature's ability to resist.
The medium itself isn't magical - in Mythic Europe parlance, silver and sunlight are mundane....which happen to have interesting properties if you hit certain supernatural creatures with them. However, it's possible to create magic sunlight and magic silver, which disappear after the duration of the spell goes away.
AM5th, pg. 85, under "The Functioning of Magic Resistance" - "Things that are created and sustained by magic (anything not created as a mundane thing by a ritual spell) are magical for these purposes."
In this case, we're talking about creating a mundane block of silver with a ritual spell, then attacking a supernatural beast that is venerable to silver with it. And then taking that process and extending it to sunlight.
This is true. You'd likely have to have some sort of storage for the sunlight (a Rego Ignem effect) that you could release in a turn, rather than create it directly. Or alternately do the ritual beforehand, and then carry it around (like a lantern.)
I meant collect natural sunlight, like a solar panel, and then have a controlled release/burn; so set up a spell on a carryable object to collect sunlight naturally (day duration), and then have it release it at the same rate once night falls. Or alternately release it all at once - but that would probably require some sort of watching ward. Personally, I allow non-ritual watching wards (as the effect specifically says that the ritual part is due to the non-deterministic nature of the ward) - so if you wanted to make a Concentration or Circle/Ring watching ward, you could; or even one that releases it all at a certain time of the evening.
A magically created medium is no longer resisted after the magic that created it is no longer active.
Of course, a medium created through hermetic magic is no longer in existence after the magic that created it is no longer active ...
... unless it was created with a ritual spell, that for most hermetic magi requires vis. I think this is what was meant.
That said, I think that hermetic magic should be capable of creating old plain sunlight rather easily, without all the fuss of going through rituals and breakthroughs concerning the lunar sphere and similar stuff. Whether sunlight created through non-ritual magic can chase away vampires with high magic resistance depends, I believe, on how it acts. If it burns them like fire, then yes, it is resisted. If it repels them like a crucifix (or like bad art repels a Jerbiton), then no, it is not magically resisted.
My instinct and preference would be you cannot create Sunlight. Or moonlight. Or starlight. A mage couldn't create 'light FROM the sun' because he's not the sun. Just like the mage couldn't magically create an arrow shot from the bow of Edgar the Grog Archer. I mean, I certainly wouldn't argue much to someone taking the stance that a Magus could use CrIg to create Light with Qualties of Sunlight, though in my own campaign it probably wouldn't work. Depending on arguments, I could pretty easily be swayed in different directions though; A specially designed spell with +1 magnitude to get it just right. Or a minor Hermetic breakthrough.
I'm inclined to also say Faeries are more likely to be susceptible to Hermetic Sunlight than demons, who may only quail before God's bright star... But at the same point, it's an emotional, mystical feel opinion, and looking at the facts would suggest that if a magus spent the requisite time to ensure their light had the correct properties (even if that was only a few extra calculations in the invention season, or if it was a whole season of experimenting, based on storyguide), then it should WORK. Basically, all the different angles and arguments seem to be valid.
Also, it does seem everyone agrees ReIg would always work to gather and release sunlight.